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We constrain cosmological parameters in flat cosmologies with tracking dark energy (or quintessence) using the existing data on cosmic microwave background (CMB) anisotropies. We perform a maximum likelihood analysis using combined data from COBE-DMR, BOOMERanG, DASI and MAXIMA, obtaining estimates for the dark energy density ₐ and equation of state wₐ, the physical baryon density ₁h^2, the scalar perturbation spectral index nₒ, the ratio R between the tensor and scalar perturbation amplitude (or the tensor spectral index nₓ). Dark energy is found to be the dominant cosmological component ₐ=0. 71-₀. ₀₄^+0. 05, with an equation of state wₐ=-0. 82-₀. ₁₁^+0. 14 (68% C. L. ). Our best fit value of the physical baryon density is in good agreement with the primordial nucleosynthesis bound. We find no significant evidence for deviations from scale invariance, although a scalar spectral index slightly smaller than unity is marginally preferred. Finally, we find that the contribution of cosmological gravitational waves is negligible. These results confirm that quintessence is slightly preferred with respect to ordinary cosmological constant by the present CMB data.
Baccigalupi et al. (Tue,) studied this question.